The invention relates to a steel truss construction method and a temporary reinforcing device used in a hoisting process of the same, wherein the temporary reinforcing device is additionally arranged on a steel truss before the steel truss is hoisted, and the temporary reinforcing device is dismounted after the steel truss is mounted in place. The temporary reinforcing device comprises two support columns which are arranged crosswise, wherein when the temporary reinforcing device is arranged on the steel truss, the temporary reinforcing device is arranged between an upper chord and a lower chord as well as between two adjacent straight web members; the two ends of the two support columns are detachably and fixedly connected onto the upper chord and the lower chord respectively; and the connection positions of one support column wtih the upper and lower chords are near the connection positions of a corresponding diagonal member with the upper and lower chords. According to the steel truss construction method and the temporary reinforcing device provided by the invention, before the steel truss is hoisted, the diagonal member is temporarily fixed by the temporary reinforcing device, so that the stress system of the whole member is not changed abnormally, therefore the integral stability and installation quality precision of the structure are ensured before the diagonal member is tensioned completely, besides, the safety in the steel truss hoisting process is improved, the construction cost is saved and the construction period is shortened.